Molecular Mechanism of Dioxin Formation from Chlorophenol based on Electron Paramagnetic Resonance Spectroscopy
Molecular Mechanism of Dioxin Formation from Chlorophenol based on Electron Paramagnetic Resonance Spectroscopy
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基于电子顺磁共振波谱研究氯苯酚生成二恶英的分子机制
DOI：
10.1021/acs.est.7b00828
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发表时间：
2017
影响因子：
11.4
通讯作者：
Xu Yang
中科院分区：
文献类型：
--
作者：
Yang Lili;Liu Guorui;Zheng Minghui;Zhao Yuyang;Jin Rong;Wu Xiaolin;Xu Yang
很少有研究对氯苯酚生成多氯二苯并对二恶英和二苯并呋喃（PCDD/Fs）的自由基中间体进行研究。本研究阐明了2,3,6-三氯苯酚（TCP）在Cu(II)O/二氧化硅基体上在298-523 K温度下热化学生成pcdd的反应途径。采用电子顺磁共振（EPR）谱法和理论计算对反应进行了研究。原位EPR表明TCP自由基（TCPR）是由TCP的氢萃取形成的。提出了在pcdd形成过程中发生的五个基本过程，包括TCPR二聚化、邻氯离子萃取、Smiles重排、环闭合和环内Cl的消除。通过管式炉热化学实验对PCDD产物的检测，进一步证实了上述机理。通过气相色谱/四极杆飞行时间质谱法检测到几种优势同源物，包括1,2,6,9-四氯二苯并-对二恶英（TeCDD）， 1,2,6,7-TeCDD, 1,2,8,9-TeCDD和1,4,6,9-TeCDD，并通过气相色谱/高分辨率质谱法进一步证实。检测到的PCDD产物符合所提出的PCDD形成机制。发现相对较高的温度会导致TCPR脱氯，形成除PCDD/Fs外的苯氧自由基。这些自由基会附着在粒子上，从而延长它们的寿命。这些反应通过分子轨道理论计算得到了进一步的验证。持久性苯氧自由基的发现因其潜在的毒性而具有重要的环境意义。该机理的细节可用于控制工业热过程中PCDD/F的形成。
Few studies have investigated the free radical intermediates involved in the formation of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) from chlorophenol. This study clarified the reaction pathways during thermochemical formation of PCDDs from 2,3,6-trichlorophenol (TCP) over a Cu(II)O/silica matrix, which was used to simulate fly ash, at 298–523 K. The reaction was studied using electron paramagnetic resonance (EPR) spectroscopy and theoretical calculations. In situ EPR indicated the TCP radical (TCPR) formed by hydrogen abstraction of TCP. Five elementary processes including dimerization of TCPR,ortho-chloride abstraction, Smiles rearrangement, ring closure, and intra-annular elimination of Cl were proposed to occur during formation of PCDDs. The proposed mechanism was further confirmed by the detection of PCDD products from thermochemical experiments in a tube furnace. Several dominant congeners, including 1,2,6,9-tetrachlorodibenzo-p-dioxin (TeCDD), 1,2,6,7-TeCDD, 1,2,8,9-TeCDD, and 1,4,6,9-TeCDD were detected by gas chromatography/quadrupole time-of-flight mass spectrometry, and further confirmed by gas chromatography/high resolution mass spectrometry. The detected PCDD products agree with the proposed PCDD formation mechanism. Relatively high temperatures were found to lead to dechlorination of TCPR to form phenoxy radicals in addition to PCDD/Fs. These radicals will be attached to particles, which will increase their lifetimes. These reactions were further verified by molecular orbital theory calculations. The discovery of persistent phenoxy radicals is of environmental significance because of their potential toxicity. The details of this mechanism could be used for controlling PCDD/F formation during industrial thermal processes.